TIME-COURSE FOR EXERCISE-INDUCED ALTERATIONS IN INSULIN ACTION AND GLUCOSE-TOLERANCE IN MIDDLE-AGED PEOPLE

The purposes of this study were 1) to investigate glucose tolerance and insulin action immediately after exercise and 2) to determine how long the improved glucose homeostatic mechanisms observed 12-16 h after exercise persist. Nine (seven men, two women) moderately trained middle-aged (51 +/- 3 yr) subjects performed 45 min of exercise at 73 +/- 2% of peak O-2 uptake for 5 days, followed by 7 days of inactivity. Oral glucose tolerance tests (OGTT; 75 g) were performed immediately postexercise (IPE; similar to 30 min) after the final exercise bout and 1, 3, 5, and 7 days after exercise. The incremental area under the plasma glucose curve was markedly higher IPE (355 +/- 82 mM min) compared with those on days 1 (136 +/- 57 mM.min; P < 0.05) and 3 (173 +/- 62 mM.min; P < 0.05). The glucose area was significantly higher on days 5 (213 +/- 80 mM.min) and 7 (225 +/- 84 mM.min) compared with those on days 1 and 3 (P < 0.05). The incremental insulin area IPE (3,729 +/- 1,104 mu U.ml(-1).min) was 43% higher compared with that on day 1 (2,603 +/- 635 mu U.ml(-1) min; P < 0.05) and 66% higher compared with that on day 3 (2,240 +/- 517 mu U.ml(-1).min; P < 0.05). The insulin area increased to 3,616 +/- 617 mu U.ml(-1).min after 5 days of inactivity (P < 0.05). An additional 48 h of inactivity did not result in any further increase in the plasma insulin response. Plasma free fatty acid concentrations were markedly higher before the OGTT performed IPE (0.79 +/- 0.07 mM) compared with those on day 1 (0.28 +/- 0.03 mM; P < 0.001) and remained higher (0.07 +/- 0.02 vs. 0.03 +/- 0.01 mM; P < 0.001) IPE at the conclusion of the OGTT. These data show an exaggerated insulin response and a marked impairment of insulin action immediately after exercise. This transient insulin resistance, which is associated with elevated plasma free fatty acid concentrations, is replaced within 24 h by enhanced insulin action and a reduced insulin response. The improved insulin action and glucose tolerance after exercise persist for 3 days but not for 5 days.